The nonskid on Marstrom's is mixture of paint and a nonskid additive (like fine sand).

I add it to the boat after painting is completed

1) mark the area that you want to be nonskid with masking tape

2) mix paint and nonskid per the instructions. If there are no instructions mix about 3 parts paint and 1 part nonskid by volume (for example 15 ml paint and 5 ml nonskid)

3) Apply the mixture to the boat using a roller

To repair a section of nonskid I mix 2 part water based polyurethane paint with nonskid and apply it using a small roller.

The non skid additive I use is Interlux nonskid additive.

These may not translate well so please post any questions you have.